Indole acetic acid modulates changes in growth, chlorophyll a fluorescence and antioxidant potential of Trigonella foenum-graecum L. grown under cadmium stress

Indole acetic acid at low (IAA(L), 10 mu M) and high (IAA(H), 100 mu M) dose-induced responses on growth, chlorophyll a fluorescence and antioxidant potential of widely cultivated Trigonella foenum-graecum L. seedlings grown under cadmium (Cd-1, 3 mg Cd Kg(-1) soil and Cd-2, 9 mg Cd Kg(-1) soil) stress were investigated. Cadmium (Cd) at tested doses reduced the growth, pigment contents, photosynthetic (O-2 evolution) and carbonic anhydrase (CA) activity which was accompanied with Cd accumulation in tissues. To quantify the performance of photosystem (PS) II, chlorophyll a fluorescence (JIP test) was analyzed and under Cd stress, the yield for primary photochemistry (phi P-0), yield of electron transport per trapped exciton (psi(0)), quantum yield of electron transport (phi E-0) and performance index of PS II (PIABS) were decreased, while it induced significant rise in energy flux parameters. Foliar application of IAA(L) dose causes significant reduction in Cd accumulation and hence alleviated the toxic effects of Cd on these parameters appreciably; while at IAA(H) dose, Cd induced-effects were further aggravated. Respiratory O-2 uptake was increased progressively with rising concentration of Cd, while together with IAA, it showed reverse trend. Cd alone and together with IAA(H) enhanced the oxidative markers: O-2(center dot-), H2O2 and MDA contents despite of the significant increase in SOD and CAT activity; while with IAA(L), these markers were declined significantly. Overall results suggest that application of IAA(L) reduced the Cd accumulation in tissues significantly; hence, increased activity of photosynthesis and antioxidant potential improved the growth performance of Trigonella seedlings grown under Cd stress.